Slides are generally stored in racks which can be inserted into a projector for their display. When a conference is prepared, the slides which are convenient for the conference in question are chosen amongst the available slides and they are arranged in a rack. There are linear racks, in which the slides are orientated all in the same way, and circular racks, in which the slides are arranged according to circle radii.
For scientific, training or advertisement conferences, such slide storing devices present certain disadvantages.
A first disadvantage consists in the fact that the slides are handled manually by the speaker when he selects the slides for a conference among the slides at his disposition. Thus, he risks to arrange them badly when returning them after the conference, which affects the repertory of the slides store. Furthermore, the capacity of the classic stacks is limited which often makes an exchange of racks necessary during the course of a conference. This is an operation which disturbs the audience and which necessitates a manual interference of the speaker or his assistant.